The Center for Particle Cosmology at Penn focuses on theoretical work at the interface of particle physics and cosmology. Penn physicists are tackling questions that range from the orgin of the early universe to the puzzles of dark matter and dark energy, using formal theory, computer simulations and analyzing data from cutting edge experiements. A summary of the research interests of the members of the Center follows; more details can be found by clicking on their web pages, or browsing our **publications**.

Prof. Mark Troddenhas worked broadly in both cosmology and particle physics, in work ranging from the structure of inflationary spacetimes to the BPS structure of intersecting branes in supersymmetric theories. The majority of his work is firmly on the particle physics-cosmology border, and includes the development of the modified gravity approach to cosmic acceleration, approaches to dark energy and dark matter; extra dimensional models of particle physics and cosmology; the baryon asymmetry of the universe; inflation and its features; and topological defects in cosmology.

Prof. Ravi Shethhas worked on physical models that describe the clustering and evolution of galaxies and other cosmological structures. He has played a leading role in the halo model, now the standard model for describing large-scale structure in the universe. Sheth has interests in statistical cosmology that span galaxy properties and their environmental dependence to predicting halo properties for precision cosmology. His work has been influential in the analysis of cosmological surveys, some of it carried out by Sheth and his wide set of collaborators.

Prof. Burt Ovrut, whose work includes the physics and geometrical structure of superstring and M-theory has a long standing interest in applying new ideas in particle physics to issues of early universe cosmology. A pioneer in the investigation of the cosmological implications of supergravity, Ovrut has explored, with collaborators, basic concepts of cosmological expansion and inflation within the context of the strongly coupled heterotic superstring and M-theory brane universes. This work led to his proposal of an alternative to inflation, called the Ekpyrotic Universe, and later refinements of this idea with important observational consequences.

Prof. Justin Khoury's research lies at the confluence of cosmology, particle physics and string theory. Recently his work has centered on devising theories of long-distance modifications of gravity and studying their observational implications. His research also focuses on alternative theories of the early universe. In particular, he is one of the pioneers of Ekpyrotic Cosmology, which proposes that the seeds of structure formation are generated before the big bang. He also introduced chameleon field theories, in which the properties of light scalar fields vary according to their environment, leading to striking predictions for near-future tests of gravity both in the laboratory and in space.

Prof. Bhuvnesh Jainhas worked on gravitational lensing and cosmology. His theoretical interests include the growth of cosmological fluctuations, nonlinear gravitational clustering and developing new probes of dark energy with gravitational lensing. Recently he has explored the observational implications of modified theories of gravity. His observational interests lie in the design of wide-field imaging surveys and the measurement of cosmological weak lensing from survey data. He is actively involved in the Dark Energy Survey, the Large Synoptic Survey Telescope and the Supernova Acceleration Probe (see below).

Prof. Mirjam Cvetichas worked on a variety of problems of elementary particle physics, particularly constructing four-dimensional solutions of superstring theory and derivations of their phenomenological implications. Cvetic’s particle cosmology work includes investigating the cosmological implications of topological solitons that may be formed within string theory.

Prof. Vijay Balasubramanian’s work in particle physics has focused on basic questions concerning the nature of space and time. Balasubramanian has worked extensively in particle cosmology, studying the nature of cosmological singularities, and investigating how cosmological observables can constrain the topology of the compact additional dimensions predicted by string theory.

**Connection to Experiments**

The theoretical studies carried out at the Center are complemented by the exceptionally strong experimental efforts in cosmology and particle physics. A distinguishing feature of our group is the close connection between theory and experiment. Penn is an active partner in a number of cosmology missions, especially in optical and sub-millimeter surveys. These include:

Euclid: A space mission to map the Dark Universe

PAPER: Precision Array for Probing the Epoch of Reionization

DES: Dark Energy Survey

LSST: Large Synoptic Survey Telescope

ACT: Atacama Cosmology Telescope

BLAST: Balloon-borne Large Aperture Submillimeter TelescopePenn’s experimental particle physics group is involved in accelerator, neutrino and dark matter detection experiments:

ATLAS experiment at the LHC (Large Hadron Collider)

DEAP/CLEAN: Direct Dark Matter Detection

SNO/SNO+: Sudbury Neutrino Observatory